Questionhi, i was reading one of your post's and it seems like you might have the knowledge i need...ok, this is my problem. with my car OFF, power, remote, and ground to my amplifier hooked up(a for SURE good ground) i get 12.6 volts...normal....but once i flip my keys forward (or backward) the voltage goes down to 3.5 ............ ive tried what seems like everything ive put an ENTIRELY different system, cd player, amplifier, power wire, a different source for the remote, totally changing everything, wires and all.. to see if it was any of my stuff doing it...with no luck. the only thing that worked was putting an old, recharged battery in my trunk for a few days...im not sure what the problem is, could it be too much stuff running off my battery, or is my battery bad...any help or ideas will be greatly appreciated!!!
AnswerHi Ryan,
Given that you have a digital multimeter available, it should be fairly simple to track down the source of your voltage drop.
My guess is that somewhere in the amplifier's power line (or the ground wiring) there's a poor connection that's causing resistance. In an electrical circuit, resistance doesn't cause a voltage drop unless there's current flowing. That's why your voltage seems fine when the car is off: the amplifier isn't drawing any current from the battery, so there's no voltage drop. When you turn the key, the amplifier switches on, current starts to flow through the power wire, and the result is a voltage drop at the point of resistance.
I'm assuming that the voltage at the battery remains at 12 volts (otherwise you'd be having problems with the other accessories in the vehicle). Somewhere, between the positive battery terminal and the amplifier's power terminal, the voltage is changing from 12 volts to 3.5 volts. You simply have to use your multimeter to test various points of the power wire until you've found the voltage drop.
Attach your multimeter's black probe to the negative battery terminal, and set the meter for DC volts. For reference, test the voltage at the positive terminal; it should be around 12.6 volts. Turn your key to "accessory" and test the voltage at the input of the power line fuse holder (which should be close to the battery). You should get the same voltage you found at the battery terminal; if it's much lower, then there may be a problem with the power wire's connection to the battery terminal itself. If it's the same, then move on to the output side of the fuse holder. If you have a voltage drop here, you may need to replace the fuse (even if it doesn't look blown) and check the connection of the wire to the fuse holder: make sure it's not corroded or charred. Keep working your way back along the power wire, paying specific attention to connection points (like fuses and distribution blocks) until you find the point of reduced voltage. Keep the black probe connected to the negative battery terminal; you may need a long jumper lead to do this. If you get to the amp, and you're still finding 12 volts on the power wire, then the likely source of the voltage drop is the ground connection.
Personally, I'm guessing that you have a problem with your fuse or fuse holder (especially if it's an AGU fuse). However, methodical testing along the power line will tell if I'm right or wrong.
Hope this helps!
Brian
